I’m not aware of a guide, but basically, you do a bootstrap, push that image to your repo, and then use ./launcher start-cmd to get the required ENV to crank up the container.
At some point you need to migate the database (if you want a zero-downtime deployment, you want to know about SKIP_POST_DEPLOYMENT_MIGRATIONS to enable you to migrate the database while the old container runs and rake db:ensure_post_migrations db:migrate after it’s launched. You also need to precompile assets and, if you’re using S3, push them there.
That’s at least most of the Discourse-specific pieces. If you would like more help and have a budget, I’m available.